If you play a normalized sine wave with 0 db (ATTRIBUTES) it is near distortion with AMP VOL = +63.
It means it is played a 0 dbFS.
You can check distortion increasing ATTRIBUTES to 0.5 db.
Same situation with same normalized sample with +12 db ATTRIBUTES, and AMP VOL = 0.
Conclusion : setting AMP VOL = 0 lowers signal with - 12 db compared to +63.
Simple no? 
Forget above Static / Flex +12 db.